Need help dont know if i could be father

Patient: Ok this girl i had sex with for one time only on may 27th 2011 says she is pregnant with my child how is this possible when the first day of her last period was april 29th and ended on may 4th and we didnt have sex until mayb 27th there is no way i can be the father right she found out she was pregnant june 16th

Doctor: You technically had sexual intercourse on may 27th during which she was in the second part of her menstrual cycle during which the chances of getting pregnant are extremely high. Thus there is a high possibility that she may be pregnant with your child. It is possible to get a paternity test done if wished. All the best.